Prior art compressors for vehicle air conditioners have cylindrical configurations. In the past, vehicle air conditioning compressors were normally ear mounted with longitudinal bolting that permitted the compressor to be pivoted to tighten the drive belt. For example, the compressor could pivot on a lower inside set of ears. A slotted arm engaged, for example, an upper outside set of ears. Once the proper belt tension was reached, the bolts were tightened to hold the position. The cylindrical shape of the compressor accommodated the arcuate slotted arm as the compressor was rotated to the proper position. The cylindrical configuration forced the through bolts that hold the compressor assembly together to lie inside the circular profile of the compressor. This presents O-ring gland sealing problems.
In modern accessory drive systems, the compressor is fixed, not pivotally mounted as described above. Belt tension is maintained by a separate spring loaded idler pulley. A modern compressor is also cross bolted. Current applications have relied on intermediate brackets between the compressor and presently available bolting points on the engine. However, motor vehicle manufacturers are planning engines that will provide standardized bolt boss configurations that will directly fit a compressor, eliminating a costly bracket and making for a more rigid and quieter application. As compressors are no longer pivotally mounted in modern drive systems, the historical reason for a cylindrical configuration is no longer valid. Nevertheless, current compressors still use the cylindrical configuration.
One newer type of automotive air conditioning compressor in use is a variable capacity, double-lobed, sliding-vane type compressor. This type of compressor has a more rectangular external configuration by moving the through bolt bosses out into the formally wasted space at the four corners. In this type of compressor, a compression housing has a chamber cavity that is oval in shape. A cylindrical rotor rotates within the chamber on a rotor shaft. The rotor has radial vanes mounted to it which slide in slots formed in the rotor. Refrigerant at suction pressure enters the compression chamber through a variable porting arrangement. The vanes compress the refrigerant, which passes outward through discharge ports in the cylinder wall past a check valve to the discharge plenum from which it exits the compressor.
Compressors of this nature usually comprise a plurality of primary components including a front head, a front side block, a cylinder block, a rear side block and a rear head. Each of these components has several bolt holes so that they may be joined together with bolts to form the compressor. The components must be sealed against one another to prevent leakage of the refrigerant working fluid to the atmosphere. These die cast components typically employ elastomeric O-rings in "as cast" grooves between the front side block and the cylinder block, and between the cylinder block and the rear side block. The front side block, cylinder block and rear side block must have metal-to-metal contact in order to hold very small dimensional clearances with internal running parts, that is, with the rotor and vanes. The small dimensional clearances control backflow leakage within the cylinder block.
Gaskets are typically employed between the front head and the front side block, and between the rear side block and the rear head to prevent refrigerant working fluid leakage to the atmosphere. Gasketed interfaces require high compressive clamping loads in order to develop an adequate bearing pressure to insure sealing. The typical bolting system holding the major components together therefore requires a large number of large diameter high tensile strength bolts. Since the bolts remain exposed to the atmosphere in the prior cylindrically shaped compressor, the elastomeric O-rings must seal around the inside of the bolt hole circle. This situation results in "as cast" grooves and O-rings configured in an irregular, that is, non-circular pattern. The irregular pattern requires that the grooves for the O-rings be cast with smooth high precision surfaces rather than be machined. It is extremely difficult and expensive to maintain an acceptable sealing surface in a die cast groove in a high production environment. Dies must be changed out within short time intervals to repair damage due to severe heat check temperature cycling and erosion. Finally, during assembly of the compressor, a liquid room temperature curing sealant is applied to the O-ring grooves as a redundant measure.
In the prior art, the weight of the cylinder block has been reduced with external depressions formed in the block during casting. The resulting thinner wall sections also reduce metal porosity and improve the structural integrity of the casting. However, such a casting die requires slides on the sides of the die, making the die expensive to manufacture and maintain. The lateral slides result in fewer cavities per die block because they take up space between the cavities.
The rotor shaft is typically supported on a bearing in the front head. Since the forward bearing and the main shaft seal need to be continuously lubricated, the prior art employs a lubricating passage extending from the intake plenum at the rear of the compressor through an axially drilled hole in the rotor shaft. A cross-drilled hole is also required at the forward end of the shaft. It is time consuming and therefore expensive to drill such holes in the rotor shaft. It is also expensive to insure the drilled holes are first free of any drilling debris and fragile burrs, and second clear of loose scale from subsequent heat treatment operations to harden, for example, the bearing journals on the shaft.